Carrier localization and recombination in InGaN quantum wells on a sub-micrometer length scale

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The physical mechanisms limiting the efficiency of light emitters (both LEDs and laser diodes) based on InGaN quantum wells are studied with an optical method (microphotoluminescence) combining high sub-micrometer spatial resolution with high spectral resolution and light gathering power. Crystal defects, indium fluctuations, and piezoelectric fields in the strained quantum wells are discussed as basic mechanisms. With a broad matrix of samples grown on different substrates (sapphire, SiC, bulk GaN) we sample quantum wells of different width, indium content, strain, and internal field for different defect densities. The low defect density of only 10 cm in the case of the GaN substrate allows studying the fluctuations and optical efficiency in larger areas free of defects as well as the impact of a single freestanding defect on the quantum well in its immediate neighborhood. This gives access to the influence of the intrinsic growth instability on fluctuations and optical properties of InGaN quantum wells.